Extruded contact electric heater strip

ABSTRACT

A thermally conductive casing and a method for forming the same for a contact heater resistance element in the form of an open extrusion of thermally conductive, soft metal which, in open form, will receive an elongate resistance element and which is then closed to confine the element and shaped into a configuration which draws the contacting edges of the extrusion into tight engagement to seal in the heating element.

United States Patent [191 Mayhew et al.

[4 1 June 12,1973

[ 1 EXTRUDED CONTACT ELECTRIC HEATER STRIP [75] Inventors: William K.Mayhew, Adrian;

' Wendell E. Disbrow, Tecumseh,

both of Mich.

[73] Assignee: Gould Inc., Chicago, 111.

[22] Filed: Mar. 23, 1972 [21] Appl. No.: 237,324

3,453,417 7/1969 l-lummel 219/536 3,387,653 6/1968 Coe 165/171 X2,875,312 2/1959 Norton.. 219/535 2,944,138 7/1960 Goff 219/540 XPrimary Examiner-Velodymyr Y. Mayewsky A ttorney-Arthur Raisch, John M.Kisselle and Robert A. Choate et al.

[5 7] ABSTRACT A thermally conductive casing and a method for formingthe same for a contact heater resistance element in the form of an openextrusion of thermally conductive, soft metal which, in open form, willreceive an elongate resistance element and which is then closed toconfine the element and shaped into a configuration which draws thecontacting edges of the extrusion into tight engagement to seal in theheating element.

3 Claims, 4 Drawing Figures [56] References Cited UNITED STATES PATENTS2,882,376 4/1959 Charbonneau 219/530 1 EXTRUDED CONTACT ELECTRIC HEATERSTRIP This invention relates to an Extruded Contact Heater Strip andMethod for Forming the Same for enclosing an electrical resistanceelement.

Circular contact heater constructions are known in the art asillustrated in a U.S. patent to Howard K. Graves, U.S. Pat. No.3,370,156, dated Feb. 20, 1968. These heaters are extensively used forapplication to the base of a compressor unit to keep the refrigerant andlubricant in said base at a predetermined temperature to preventdeleterious effects caused by frothing and foaming. In other instances,the heaters are used on oil sumps and other places where extreme coldtemperatures are to be moderated, for example, in internal combustionengine crankcases and so forth.

One of the problems in forming these strip contact heaters is thesealing of the electrical resistance units which are generally a finewinding of resistance metal around a core covered with an insulation.

It is an object of the present invention to provide a relatively simplecontainer for the resistance elements which has an adequate contactsurface for a cylindrical container to be heated and which isself-sealing to the point that the electrical resistance heater is wellprotected within the casing.

It is a further object of the invention to provide an extruded sectionwhich can be readily cut in proper lengths to receive resistanceelements and which can then be closed and subsequently formed in acircular configuration to enhance the closing action and insure a tightseal.

Other objects and features of the invention will be apparent in thefollowing description and claims in which the details of theconstruction are set forth together with the principles of operation inconnection with the best mode presently contemplated for practice of theinvention.

Drawings accompany the disclosure and the various views thereof may bebriefly described as:

FIG. 1, an elevation of a completed unit showing the final configurationpartially in section on line 11 of F IG. 2.

FIG. 2, a sectional view on line 2-2 of FIG. 1.

FIG. 3, a sectional view of the extrusion used in the practice of theinvention.

FIG. 4, a sectional view of the extrusion in closed position.

REFERRING TO THE DRAWINGS In FIG. 3, an extrusion is shown incross-section, this being formed of a soft aluminum alloy, that is, inannealed condition. Aluminum alloy 1100 is suitable.

It will be noted that this extrusion shape has a base portion with abottom surface 12 which is straight in cross-section such that it willbe a contact surface for a cylindrical wall after the device iscompleted. Opposite to the contact surface 12 is a recess 14semicircular in shape formed by two sides 16 and 18 rising from the base10. The side 18 terminates at an edge 20 which is fairly broad andslightly rounded. The side 16 continues in a curved extension portion 22integrally joined with the side 16 having a free edge 24 and shaped toprovide a recess 26.

A small concavity 28 is provided at the juncture of the wall 16 with theextension 22 to facilitate a bending action. The extrusion is made to befinally shaped into the configuration shown in FIG. 4 where the edges 20and 24 are brought into contact to merge the two recesses 14 and 26 intoan elongate tubular opening.

The steps in the construction of the unit are, first, the extrusion ofthe section shown in FIG. 3. Secondly, a wound resistance element 30 islaid into the opening 14 after a section of the extrusion has been cutto length. The resistance element 30 preferably has leads 32 and 34connected to its ends with a suitable sealing between the insulatingcovers of each. The open extrusion is then rolled or otherwise movedinto a closed position as shown in FIG. 4, the soft materialfacilitating this closure to a relatively tight joint between the edges20 and 24.

Fastening elements are then attached to each end of the tube as shown inFIG. 1, namely, elements 40 and 42, these having an open ferrule collarwhich is crimped tightly around the ends of the closed tube to compressthe insulation of the lead wires and create a tight seal. Each fasteningelement has an extension which serves as a part of a tightening clampassembly. Extension 44 on the crimped section 40 has folded parallelwalls 46 and a cross-over fold 48, to parallel walls 46, fold 48being-apertured to receive a screw 50 having a head 52 and carrying awasher 53. On the crimped section 42 is an extension 54 having a base 56and two side walls 58. The edges of the parallel side walls 58 areangled as shown at 60 to cooperate with a separate lock plate 62 havinga threaded opening 64 to receive the threaded end of the tightening bolt50. A tab 66 is provided on the plate 62 for a grounding connection ifthis is desired.

As the assembly is viewed in FIG. 1, it will be seen that the tighteningof the bolt 50 will cause the lock plate 62 to clamp behind the edges 60to draw the ends of the heater strip together. After end portions 40 and42 are applied to the closed extension, the device is formed into afinal configuration as shown in FIG. 1, that is, the flat base portionis placed on the inside and the device is formed into a final shape.

It will be noted that the juncture 20-24 is approximately on or a littleabove the center line of the diameter of the enclosed recess, whichcenter line is substantially parallel to the base 12. The distance fromthe base is designated at the dimension A in FIG. 4. Thus, when theclosed straight extrusion is formed into the final shape shown in FIG.1, there will be a tendency on the part of the metal near the base tocontract and the metal near the outer diameter to stretch. This causes acompression action on the leading edge 24 of the extension 22 so that itis brought into tight engagement with the top side wall 18 of the base.Thus, when the forming is complete, it is almost impossible to detectthe joint at this area. The recess in the strip is, therefore, tightlyclosed and sealed. The assembly is made in lengths which areapproximately the circumference of a container to be heated and they maybe applied by slipping over the container with a tightening action byreason of the screw clamp shown in FIGS. 1 and 2. This brings the fiatsurface 12 in tight contact with the walls of the container to be heatedand the soft material allows the strip to conform itself closely to thewalls to provide an excellent heat transfer from the enclosureresistance element to the embraced container.

We claim:

1. A contact electric heater strip comprising an electrically insulated,elongate resistance heating element surface on an inside, said basehaving side walls extending upwardly from the base to approximately adiameter of said cylindrical recess which is parallel to said base, andan integral, semi-circular extension on one of said walls arching oversaid recess with a free edge to contact a top edge of said other side toprovide a closed, elongate, circular recess for containing a heatingelement, said closed extrusion being adapted to be bent around an axisspaced from said base away from said recess wherein said free edge isdrawn tight againstsaid other side.

2. The contact electric heater strip as defined in claim 1, wherein theformable metal is of annealed aluminum.

3. The contact electric heater strip as defined in claim 1, wherein theformable metal is of dead soft metal material.

1. A contact electric heater strip comprising an electrically insulated,elongate resistance heating element and an elongate casing tightlyenclosing said heating element, said casing comprising an integral,elongate, extrusion formed of a highly thermally conductive, formablemetal, said extrusion having in cross-section a base formed with a flatcontact surface on an outside and a semi-circular, cylindrical recess onan opposed surface on an inside, said base having side walls extendingupwardly from the base to approximately a diameter of said cylindricalrecess which is parallel to said base, and an integral, semi-circularextension on one of said walls arching over said recess with a free edgeto contact a top edge of said other side to provide a closed, elongate,circular recess for containing a heating element, said closed extrusionbeing adapted to be bent around an axis spaced from said base away fromsaid recess wherein said free edge is drawn tight against said otherside.
 2. The contact electric heater strip as defined in claim 1,wherein the formable metal is of annealed aluminum.
 3. The contactelectric heater strip as defined in claim 1, wherein the formable metalis of dead soft metal material.